looking to take HELOC or HELOAN on 2 family rental property

[Chris Turek]

Looking for information and advice. I have a 2 family on north Jersey. I have a mortgage at 3.5% and owe about 500k on it. I believe the house would appraise for over 900k, but let's assume 900 for this post. I am looking to understand how much I could take out or max LTV either way on a HELOC or equity loan. Also, assuming if a lender went to 85 or 90% LTV the rate would take a hit, how much could I take out at whatever the best rate is? I have excellent credit and financials so FICO or DTI should both be good. I'm assuming it wouldn't make sense to refi as I would be giving up the 3.5% rate I have but if someone has facts that lead to a different answer I'm open to that as well.

Thanks

Chris